The difficulties of achromatization in the deep ultraviolet are known. Except for quartz glass, essentially only crystalline materials are available. Here, problems are caused by the anisotropy of the crystals which, in addition to the double refraction, also leads to poor manufacturability of polished curved surfaces. In addition, the possible materials are poorly resistant to environmental influences.
This is described in U.S. Pat. No. 5,028,967. Here, as a solution to the problem, the use of SiO.sub.2 glass with GeO.sub.2 admixed (also together with boroxide) is given. What is claimed is a GeO.sub.2 content up to 50 mol %. The example having the highest GeO.sub.2 content has 13.5 mol % GeO.sub.2 and preferably, the content is up to 30 mol %. The deviations of the index of refraction, dispersion and Abbe number compared to pure quartz glass are small. Accordingly, the achromatization is difficult.
The production of amorphous germanium oxide from colorless glass is known per se, for example, from Ullmann's "Encyklopadie der technischen Chemie", 4th edition, Volume 12, Weinheim New York 1985, article "Germanium und Germanium-Verbindungen", pages 221 to 226, key word "Germaniumdioxid", page 225 and from the FR-A 20 18 484 which is cited there (page 1, lines 12 to 19, corresponding search report, as well as title and short analysis of the citation "Secrist and Mackenzie").
In one version, crystalline GeO.sub.2 is generated from GeCl.sub.4 by hydrolysis, melted and rapidly cooled down. This serves as an input material for milling as a powdered catalytic material. From an oxygen plasma having C.sub.2 H.sub.5 OGe, Secrist and Mackenzie allow GeO.sub.2 to deposit onto a cooler base from the gas phase and thereby generate a non-crystalline film.
GeO.sub.2 glass bodies are, however, not known as usable lens blanks.
In the above-mentioned text of Ullmann, key word "Germanate", page 225, optical glasses of germanates, for example, Zn.sub.2 GeO.sub.4, are known which have a high refractive index.